First Online: 07 December 2005Received: 18 July 2005Accepted: 07 December 2005

Abstract

BackgroundTwo closely related species Burkholderia mallei Bm and Burkholderia pseudomallei Bp are serious human health hazards and are potential bio-warfare agents, whereas another closely related species Burkholderia thailandensis Bt is a non-pathogenic saprophyte. To investigate the genomic factors resulting in such a dramatic difference, we first identified the Bm genes responsive to the mouse environment, and then examined the divergence of these genes in Bp and Bt.

ResultsThe genes down-expressed, which largely encode cell growth-related proteins, are conserved well in all three species, whereas those up-expressed, which include potential virulence genes, are less well conserved or absent notably in Bt. However, a substantial number of up-expressed genes is still conserved in Bt. Bm and Bp further diverged from each other in a small number of genes resulting from unit number changes in simple sequence repeats ssr in the homologs.

ConclusionOur data suggest that divergent evolution of a small set of genes, rather than acquisition or loss of pathogenic islands, is associated with the development of different life styles in these bacteria of similar genomic contents. Further divergence between Bm and Bp mediated by ssr changes may reflect different adaptive processes of Bm and Bp fine-tuning into their host environments.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2164-6-174 contains supplementary material, which is available to authorized users.